Recent developments in electronic devices have created a demand for power devices that can supply higher currents. In addition to higher currents, it is important for power devices to operate more efficiently.
One way of obtaining efficiency is to operate the power device at higher frequencies. Conventional silicon based high voltage power switching devices such as 600V MOSFETs exhibit desirable high frequency switching characteristics. However, when conducting more than 5 A of current high voltage MOSFETS exhibit excessive power loss, and thus poor efficiency.
On the other hand low voltage power switching device can operate more efficiently at higher currents. The low breakdown voltage rating of low voltage power MOSFET is, however, a draw back.
To take advantage of the efficiency of a low voltage power MOSFET, the prior art has proposed combining a high band gap device with a low voltage device. For example, the prior art literature has proposed connecting a low voltage power MOSFET in a cascode arrangement with a high band gap device. According to the prior art concept, the high band gap device is selected to withstand a large portion of the reverse voltage, which allows for the selection of a low voltage power MOSFET.
A low voltage power MOSFET typically exhibits lower resistance during operation (Rdson) compared to a high voltage power MOSFET. High band gap devices, however, exhibit higher Rdson. The higher Rdson is due to the low carrier (electron) mobility of the high band gap material that comprises the high band gap device, which is usually higher than silicon. Thus, when a low voltage silicon based MOSFET is combined with a high band gap device, the advantageously low Rdson of the silicon-based MOSFET is sacrificed.